It is known to employ ultrasonic sound to drive pests away from selected areas (e.g. Quittner U.S. Pat. No. 3,138,138). It is also known to employ air scoops on moving vehicles to energize horns for warning persons of the approach of the vehicle. However, it is not known to provide a vehicle-mounted scoop-energized ultrasonic device that can be continually operated, without human annoyance, for scaring birds and/or animals away from the path of the moving vehicle. It is accordingly the object of the present invention to provide an accessory of this type which is of simple and inexpensive yet highly effective construction.